Unique Sensitivity to Extracellular Proteases and Peptide Protection of the HERG Potassium Channel

Abstract

The human ether‐a‐go‐go–related gene (hERG) encodes the pore‐forming subunit of the rapidly activating delayed rectifier potassium channel (IKr), which is important for cardiac repolarization. Dysfunction of hERG causes long QT syndrome, arrhythmias and sudden death, which occur in patients with cardiac ischemia. Cardiac ischemia is also associated with activation of various proteases. We characterized the effects of proteases on hERG/IKr with the aim to develop novel strategies to prevent protease‐mediated damage. Using whole‐cell patch clamp and Western blot analysis we demonstrated that the hERG/IKr channel is selectively cleaved by the serine proteases, proteinase K and protease XXIV. Using molecular biology including making chimerical channels between protease K‐sensitive hERG and insensitive hEAG, we identified that the S5‐pore linker of hERG is the target domain for proteinase K. We discovered that the scorpion toxin BeKm‐1, which binds to the S5‐pore linker of hERG, can effectively protect hERG from proteinase K‐mediated damage. The reduction in mature ERG expression was observed in a rabbit cardiac ischemia model and in hERG‐HEK cells cultured in hypoxic conditions. BeKm‐1 effectively prevented the hypoxia‐induced reduction of the mature hERG expression. In conclusion, hERG is uniquely susceptible to proteases, which may contribute to arrhythmias under conditions such as cardiac ischemia. Protecting hERG channels from proteolytic damage using specific peptides may represent a novel strategy to prevent and treat arrhythmias associated with ischemic heart disease.(Supported by the Canadian Institutes of Health Research & the Heart and Stroke Foundation of Ontario)